1. Field of Invention
The area of utility of the invention comprises prevention of development of system instability within power systems when threatened by transmission line faults, and certain other system stability endangering events.
The area of method comprises responding to faults, and other events that could endanger system stability, by rapidly initiating preprogrammed processes of
a. full or partial fast closure of intercept valves of steam turbine type generator prime movers of power systems, preferably effected within 1/4 second, PA1 b. subsequent partial reopening of intercept valves, preferably so effected that the valves begin to reopen somewhat in advance of occurrence of the peak and the first forward swing of the generator rotor, and substantially attain planned full extent of partial reopening within a fraction of a second following that peak. PA1 "I propose to avoid operation of the high pressure safety valves by providing fast acting and fully commercially available dump valves, which are programmed by the fast turbine control system to dump high pressure steam, either to atmosphere, or preferably, to the turbine condenser, with concomitant supply of spray water for cooling purposes." the idea being to employ enough dump valves to eliminate lifting of safety valves. PA1 "Also, it will be clear that where a sudden, sustained drop in driving power of a reheat type turbine is wanted, it will be only feasible to achieve desired results by using the intercepting valve as a steam flow modulation device to supplement control valve modulation of steam flow to the high pressure turbine which, however, it is judged can be accomplished by those skilled in the art merely with application of generally known practices (21, 22)." PA1 a. as in Continental European type once-through fossil fuel and also HTGR, high temperature gas cooled reactor type nuclear installations, the high pressure turbine is provided with a by-pass to the cold reheat line, PA1 b. in those nuclear installations in which extent of reheat is slight, and there is therefore no problem of protection of the reheater from overheating, PA1 c. when control valves either are held open, or are first rapidly fully or partly closed, and then fully opened, PA1 d. sustained .Iadd.partial .Iaddend.control valve closure is employed and is supplemented by initiation of a reduction in rate of steam generation within the steam supply source, PA1 a. high pressure steam, or PA1 b. low pressure steam. PA1 1. the post-fault or more generally the post stability endangering event driving power of the turbine or turbines down stream of the intercept valve or valves will exceed the pre-fault, or pre-event driving power, a circumstance which tends to adversely affect system stability, this being especially the case when the fault or other stability endangering event results in the sustained opening of one or more transmission system circuit breakers, and thereby operates to impede transmission of power in the post-fault or post-event regime, whereas actually it would normally be advantageous for the total post-fault or post-event driving power of the turbine to be held less than, and, as a rule, preferably somewhere in the range of 60 to 90 percent of pre-fault or pre-event value, PA1 2. reheat and MSR (moisture separator and moisture separator reheater) pressure safety valves may discharge steam and in some cases may thereafter leak and require maintainance. PA1 1. intercept valve closure which are fast enough and sufficient in extent to have a favorable effect on generator rotor first swing stability, and preferably take the form of full closure effected in 1/4 second or less, PA1 2. subsequent reopening of some or all intercept valves to a partially open position with reopening preferably initiated somewhat in advance of the first forward swing of the generator rotor, and carried to completion within a fraction of a second following the peak of that swing, PA1 3. preprogrammed servo valve implemented retention of partially opened intercept valves in, or substantially in, the preprogrammed position that they attained in their rapidly executed reopening process, PA1 1. full or partial closure followed by full reopening, PA1 2. full or partial closure followed by partial reopening, PA1 3. partial closure. PA1 a. fully closing all intercept valves in a fraction of a second by rapidly opening valve actuator oil dump valves, PA1 b. fully or partly closing all intercept valves under servo control, PA1 c. after initial full or partial closure of all intercept valves, repositioning under servo control, PA1 d. supplementing item (c) by fast partial intercept valve reopening initiated somewhat in advance of the generator rotor first forward swing, preferably effected within 1/2 second, with control of extent of reopening determined with use of metering cylinders or with servo or cam operated valves, PA1 e. fully closing all or some control valves in a fraction of a second by rapidly opening valve actuator oil dump valves, or PA1 f. fully or partly closing all control valves under servo control, PA1 g. after initial full or partial closure of control valves, fully or partly reopening under servo control PA1 h. supplementing item (g) by fast full or partial control valve reopening initiated somewhat in advance of the instant of generator rotor first forward swing, and preferably effected within 1/2 second.
The preprogrammed processes (a) and (b) may optionally be supplemented by other control measures, such as, but not limited to, control valve repositioning and initiation of change in rate of steam generation by steam supply sources, but employment of such supplemental measures is not requisite.
2. Prior Art
This invention is similar to, but can be viewed as, in certain aspects, more basic than that disclosed in the writer's copending application Ser. No. 388,619, now U.S. Pat. No. 3,848,138.
To ensure adequate description of the prior art, the presentation contained in U.S. Pat. No. 3,848,138 is to be regarded as incorporated in this application by reference.
To aid in clarifying how the prior art relates most closely to this application, it has appeared to be desirable to review what was involved in the total process of invention under several headings, as in what follows.